This invention relates to electrically conductive compositions exhibiting superconductivity or superconductor-like behaviour.
It is known that certain ceramic compositions become superconductive with transition temperatures which are as high as 98K. The composition YBa.sub.2 Cu.sub.3 O.sub.7-x, for example, exhibits this effect and has been closely studied. The mechanism by which superconductivity is achieved is not fully understood but it is believed that the appearance in the Perovskite structure of planes containing only copper and oxygen, is of critical importance. Other ceramic compositions showing this structural feature have been found to exhibit superconductivity and examples can be quoted of La-Ba-Sr-Cu-O; La-Ba-Cu-O, Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O. The attainment of superconductivity at still higher temperatures has been reported in certain compositions but the results are not readily reproduceable.
It is an object of one aspect of this invention to provide a ceramic composition exhibiting superconductivity, or superconductor-like behaviour at temperatures significantly in excess of 98K.
According to a first aspect of this invention, there is provided a ceramic material containing copper, characterised in that copper ions are maintained substantially independently of temperature in an oxidation state providing a significant population of Cu(I), the material exhibiting superconductivity or superconductor-like behaviour at temperatures in excess of 200K.
Advantageously, the material has the Perovskite structure.
Preferably, the material has a crystal structure with planes comprising substantially only copper and oxygen atoms.
In a further aspect, the present invention consists in a method for use with a composition which exhibits superconductivity below a superconducting transition temperature, characterised by the step of maintaining at least a proportion of a metallic species in the composition in a reduced state, and thereby causing the composition to exhibit superconductivity or superconductor-like behaviour at a temperature significantly in excess of the superconducting transition temperature.
Advantageously, the method comprises chemically or electrochemically reducing said metallic species.
In a still further aspect, the present invention consists in a conductor exhibiting superconductivity or superconductor-like behaviour at room temperature and comprising a ceramic composition containing a reduced metal species maintained in an environment serving to prevent or inhibit oxidation of said species.
Advantageously, the reduced metal species comprises Cu(I).
In yet a further aspect, the present invention consists in a superconductor comprising a ceramic composition being the negative electrode of an electrochemical cell.
Advantageously, the ceramic composition comprises planes containing substantially only copper and oxygen.